The present invention relates to a pressure-controlled valve device with an opening pressure which can be switched to low pressure and high pressure on the cooling fluid circuit of an internal combustion engine, particularly for a motor vehicle, and, more particularly, to a valve device is equipped with two spring-loaded moving closing bodies and is subjected from inside a cooling fluid container to pressure, depending on the operating condition of the engine, by gas emerging or vapor emerging from the cooling fluid (gas pressure load), on one hand, or by the cooling fluid itself (cooling fluid pressure load), on the other hand, and which opens at a higher pressure when subjected to fluid pressure than when subjected to gas pressure because of control by way of a float which can be raised with an increasing cooling fluid level.
A valve device is shown in DE 34 36 702 C2 which permits the cooling fluid circuit to be safeguarded with, on one hand, one operating pressure (low pressure) during the operation of the engine and, on the other hand, an increased pressure (high pressure) after the engine operation has been switched off. This prevents ejection of cooling fluid when the hot internal combustion engine has been switched off and the coolant circulation is interrupted. An increase in volume caused by the formation of an emergent such as vapor occurring locally does not then lead to an ejection of coolant. In the case of a cooling fluid volume increased beyond the engine operating condition, an additional pressure valve located in a float is connected upstream of the low-pressure valve adjusted to the operating pressure, with the two excess pressure valves being connected in series in this condition. Because of the series connection, the excess pressure valve in the float is only subjected to a relatively small closing force; this closing force corresponds to the difference between the opening pressure of the excess pressure valve located outside the float and that for the high pressure above atmosphere determined for the cooling fluid container when the engine is at rest. Should the high pressure in the cooling fluid container be, for example, 2 bar and the low pressure during engine operation be 1.4 bar, the closing pressure of the valve in the float is dimensioned at 0.6 bar. In the case of valves with a low closing pressure, high manufacturing accuracies are necessary for satisfactory operation, particularly with respect to the closing spring. In the known device, furthermore, two excess pressure valves are necessary with mutually independent structures and separate valve parts in each case, in particular separate closing springs. A similar device is shown in from DE 34 39 554 A1.
The present invention has an object of providing a simpler valve device which, with less manufacturing outlay, still operates reliably. In order to be able to reduce the manufacturing accuracy required for the springs and to be able to increase the functional reliability of the valve, one specific objective is to use few valve parts as possible and to have springs which do not have to be configured for a small pressure difference of the valve. In addition, the valve springs should, if possible, not be surrounded by the cooling fluid so that the springs are not subjected to the danger of sludging up and corrosion with the consequence of functional impairment.
The foregoing objectives have been achieved in accordance with the present invention by providing that the low-pressure closing body which determines the function when the device is subjected to gas is the support for the high-pressure closing body (16); when the float is raised, the flow path whose flow is controlled by the low-pressure closing body is shut off and a flow path leading through the low-pressure closing body to the high-pressure closing body is open; the closing pressure to which the closing bodies are subjected is introduced exclusively via the high-pressure closing body; the resultant effective area determining opening of the low-pressure closing body taking place under the control pressure is, under all operating conditions, greater than that for opening of the high-pressure closing body; and when the high-pressure closing body is open, the low-pressure closing body has a defined open position.
In a device constructed in such a way, the two valves controlling the high pressure and the low pressure are integrated into a common unit in which the closing force for both valves is applied by a common spring. Because the two valves act in a parallel connection in the arrangement according to the invention, the closing pressure of the spring corresponds to the total difference between the high pressure within the cooling fluid container and the atmosphere. The closing pressure which has to be applied by the common spring is, therefore, within a range for which small manufacturing inaccuracies in the production of the spring only affect the functional accuracy of the valves to an extremely small extent.
A particularly advantageous embodiment of the valve device according to the invention is one in which the low-pressure closing body has an annular peripheral sealing flange protruding radially outwards which can be seated so as to seal against the valve outlet flow direction on a valve seat permanently attached within the valve housing and which is connected radially outwards in a gas-tight manner to the valve housing by a sealing element substantially free of reaction forces. A low-pressure flow path emerging into the cooling fluid casing exists between the diaphragm and the sealing flange. The low-pressure flow path is tightly separated from the inside of the cooling fluid casing when the float is raised. The low-pressure closing body also has a high-pressure flow path connecting the cooling fluid container to atmosphere when the high-pressure closing body is open. Practically frictionless motion of the low-pressure closing body is possible by using a sealing diaphragm to form the two separated flow spaces within the closing body of the low-pressure valve.
A non-return valve opening in a corresponding manner can be introduced quite simply into the high-pressure closing body for pressure balance from the outside to the inside.